Southern California -- this just in

The suspect in the slaying of 12 people at a screening of "The Dark Knight Rises" at a Colorado movie theater left little record of his thoughts or activities online, with no Facebook, Twitter, LinkedIn or Myspace accounts under his name.

Few details in the emerging sketch of James E. Holmes — the 24-year-old alleged to have killed at least 12 people and injured 58 others in Aurora — offer any answer to the question Americans find themselves once again asking after a shooting rampage: Why?

Friends and neighbors were baffled, and Holmes left no clues online as to his potential motives or mental state. He had no criminal record. Authorities say he booby-trapped his apartment in Aurora with explosives and chemical devices, and they were still working to disable them Saturday before they could collect evidence that might yield insight into his thinking.

The suspect had been pursuing a doctorate in neuroscience at the University of Colorado Denver Anschutz Medical Campus in Aurora for a year, but had begun the process of withdrawing from the program last month, officials said. It is not clear what triggered his decision to drop out, although some reports suggested he was having troubles with his studies.

A neighbor described Holmes as a very shy, well-mannered young man who was heavily involved in the local Presbyterian church.

"He seemed to be a normal kid. I don't know what triggered it," said Tom Mai, a retired electrical engineer. "This makes me very sad."

His comments were echoed by many who had passing acquaintance with Holmes. Few seemed to know him intimately, but he was not totally withdrawn; he had friends and played sports. His junior varsity soccer photo shows him looking confidently into the camera wearing his No. 16 jersey.

One fellow Westview High School student, who asked not to be identified, listened as people reviled the suspect all morning, and only at lunch did he learn they were talking about his old classmate.

"I got a call from another friend who asked, 'Do you know who it is? Jimmy Holmes,'" he said. "I was silent and no longer hungry."

He said he and Holmes were part of a four-person group that ate together during their sophomore and junior years. "We had the same humor," the friend said. "We were all people who didn't have go-to best friends, so we all ate lunch together."

He said that Holmes had a "dark, sarcastic kind of humor" but that he never "read it as psychotic," and he wasn't noticeably introverted within their circle.

"Looking back, I guess he was dorky, and so was I. He wasn't quiet, but he didn't make a big effort to make friends."

UC Riverside Chancellor Timothy P. White said Holmes was an honor student as an undergraduate there. He had no run-ins with police on campus or anything else that would foreshadow what happened. White said professors who knew Holmes expressed disbelief about what occurred.

"We are very deeply saddened by this horrific event," he said.

He said neurological sciences is a rigorous area of study on campus. "He was an honor student, so academically, he was at the top of the top," he said.

Jessica Cade, 23, a graduate student at UC Riverside, lived in the same honors dorm as Holmes and said that she would occasionally go out with him with friends.

"He was a very nice guy. He was very, very smart; a little weird — kind of like you'd expect a really smart guy to be," Cade said. She said that Holmes and other young men in the dorm often played video games, especially Guitar Hero, but nothing out of the ordinary.

"They're calling him 'deranged' and a 'lunatic.' Never in a million years would that have crossed my mind," Cade said. "I was horrified when I saw his picture on the news. I was very close to fainting in the office."